Many instruments and equipments can work properly only when they are put horizontally, such as electronic balances (i.e., weighing instruments) operating based on gravitation. There are errors when a balance is inclined. The more inclination the balance has, the larger the errors are. To maintain a certain level of precision, the balances must be kept within a certain horizontal range. Therefore, each of the balances is equipped with a bubble level and adjustable feet comprising height adjustment screws. Bubble levels comprise a sealed housing that is partially filled with liquid and contains a gas or air bubble. The upper part of the housing comprises a transparent window. The inside wall of the transparent window is a curved surface with a large radius. The gas bubble is located in the center of the bubble level when the device is aligned horizontally. The position of the gas bubble will move towards an upper direction when the device is inclined and not aligned horizontally. Users may observe the air bubble position, which indicated the inclined status of the electronic balance via the transparent window above the housing. Users may change the level status by adjusting the height of the adjustable feet by rotating the adjustment screw threads while observing the position of the gas bubble in the electronic balance until the gas bubble is located in the center of the bubble level.
Usually there is a marking circle on the transparent window of the bubble level. The level status is out of an acceptance range when the edge of the gas bubble exceeds the marking circle, and the weighing error will be too large, and the result will be unreliable. As a result, users have to position the gas bubble back into the marking circle, and preferably back to the center, by adjusting the level status.
It is well-known that three points can determine a plane. Therefore, a device that requires adjustment of the level status, such as an electronic balance, normally has three supporting points (i.e., three feet). One of the three feet is fixed, while the other two feet are adjustable. However, to those users who are less experienced, it is very difficult to adjust the level status by adjusting the height of those two feet based on the position of the gas bubble. Due to the triangle shape caused by the three feet, when the height of one foot is adjusted, the gas bubble moves in a diagonal direction. It is very inconvenient for the users.
Thus, an apparatus for automatically adjusting the level by motor control is contemplated. Or it is contemplated to send out an alarm as the gas bubble exceeds the marking circle so that the users may be prompted to roll the two adjustable feet to adjust the level status according to the position of the gas bubble. It is also contemplated to correct the weighing results according to the relationship between the incline status and weighing errors, and make the weighing results more precise by correcting the weighing results. Due to these and other reasons, it is desired to obtain the electronic data (value) of the level status (inclining status). A motor control system can determine how to adjust the mechanism only if it received the electronic signal or data of the level status. Patent CN100362326C discloses how to use electronic tilt sensor for alarming, amending the following weight, starting automatic calibration, and start the leveling guide, etc.
There are various methods and apparatuses for measuring the level status in the prior art.
Patent CN202204509U discloses a gas bubble electric-potential-type level sensor. Each electrode receives a different electric potential when the gas bubble is in different positions. The position of the gas bubble can be deferred from different electric potentials of electrodes. However, the liquid filled in the sealed housing must be conductive, and the electrodes also have to be inserted into the bubble level. It makes the manufacturing process very complex and is costly. The electrodes obstruct the visibility of the air bubble and interfere with users' observations.
Patent CN1645070A, i.e., US7325321 B2, discloses a method and apparatus for aligning an electronic balance. An inclination sensor is a gas-bubble-type level. A light-emitter emits light downwards from the top of a bubble level. There are at least three receiving devices installed below the bubble level. However, the light-emitter installed on the top influence the users' observations of the gas bubble to a certain extent.
Patent DE3234372A1 discloses a balance with an electronic inclination sensor. This electronic inclination sensor is a gas-bubble-type level. A light emitter emits the light upwards from the bottom of a bubble level. Receiving device(s) is installed at the upper of the bubble level, and severely interferes with users' observations of the gas bubble.
Patent JP58033114 discloses an apparatus with a gas bubble level. It is equipped with a lighting cell on one side and a plurality of optical sensors on the other side. This apparatus has a transparent cube. The lighting cell is installed on one side of the cube, while the plurality of optical sensors are installed on the other side of the cube. Due to the cubic structure, this apparatus is not suitable for 2-D level status.